old string: ?a? ?b? ?c?
 one --- 
String is now aRep bRep cRep
 two --- 
String is now "aRep" "bRep" "cRep"
 Comparison --- 
Benchmark: timing 100000 iterations of IMP_REPLACE, STD_REPLACE...
IMP_REPLACE:  0 wallclock secs ( 0.10 usr +  0.00 sys =  0.10 CPU) @ 1000000.00/s (n=100000)
            (warning: too few iterations for a reliable count)
STD_REPLACE:  6 wallclock secs ( 4.99 usr +  0.00 sys =  4.99 CPU) @ 20040.08/s (n=100000)